For example, Patent Document 1 proposes heating a mixture of a gaseous organic transition metal compound, a carrier gas and a gaseous organic compound to 800-1300° C. for producing a vapor deposition carbon fiber in suspension.
Patent Document 2 proposes a method for synthesizing a carbon nanotube including the steps of: forming a catalytic metal film on a substrate; etching the catalytic metal film to form separated catalytic metal nanoparticles; and supplying a carbon source gas into a thermochemical vapor deposition system to grow a carbon nanotube on each of the separated catalyst metal nanoparticles by thermochemical vapor deposition, thereby forming on the substrate a plurality of aligned carbon nanotubes perpendicular to the substrate, where the step of forming separated catalytic metal nanoparticles is performed by gas etching, where an etching gas, which is one selected from the group consisting of ammonia gas, hydrogen gas and hydride gas, is pyrolyzed to be used.
Patent Document 3 proposes a method of vapor-phase synthesizing a single-layer carbon nanotube by directing a hydrocarbon gas together with a carrier gas onto a base including a thermoresistant porous body carrying dispersed catalytic microparticles and utilizing pyrolysis of the hydrocarbon gas.
Patent Document 4 proposes a method of manufacturing a carbon nanotube on a metal surface using chemical vapor deposition by heating the metal and flowing toward it a gas which serves as a carbon source, characterized in that the metal surface has fine asperities provided by oxide microcrystals on the metal surface.
Unfortunately, conventional methods such as those in Patent Documents 1 to 4 produced carbon-containing by-products such as amorphous carbon or graphite in addition to desired carbon nanotubes. They also produced carbon nanotubes with large variation in their diameter, making it difficult to manufacture homogeneous carbon nanotubes in a stable manner.
Carbon nanotubes may have varying diameters due to the variation in size of catalyst particles. When catalyst particles are formed by a chemical method such as pyrolysis, it is difficult to control their shape, resulting in a morphological variation among them. Aggregation of catalyst particles may also cause a morphological variation. Further, varying growth rate of carbon crystals on catalyst particles also tends to cause varying shapes of the resulting carbon nanotubes.
In addition, the use of particulate catalyst does not allow easy production of a carbon nanotube with larger length.
Patent Document 1: Japanese Patent Laying-Open No. 60-54998
Patent Document 2: Japanese Patent Laying-Open No. 2001-20071
Patent Document 3: Japanese Patent Laying-Open No. 2002-255519
Patent Document 4: Japanese Patent No. 3421332